Content, such as digital data, is comprised of bytes of information, with each byte representing, in some sense, a sample of source data at a particular point in time and/or space. There is usually some type of redundancy in such data. As is well known, this fact is used to compress the data to make it more efficient for data transmission and storage.
In addition to data redundancy, data importance is another factor present in such data. In other words, some parts of the data are more important than others, from the point of view of human perception of the data.
One type of content is digital images. Digital images are comprised of pixels, with each pixel represented by one or more bytes of information. For typical color images, 3 color components (usually Red, Green and Blue) are needed, with each component typically represented by one byte of information. Hence, color images can be adequately represented by 3 bytes of information for every pixel in the image.
The number of pixels in an image is determined by the resolution of the image. A 1-MegaPixel image contains one million pixels. The amount of information carried by a 1-Mega Pixel color image is, therefore, of the order of 3 Megabytes. Today's digital cameras generate images much higher in resolution. A 6-Mega Pixel color image would translate to about 18 MB of data. Since digital images carry so much information and take up lots of space, it is only natural that techniques are developed to compress the large of amount of image data.
The JPEG (Joint Photographic Experts Group) standard is an image compression standard that was standardized in 1992, and is the most commonly used method of compression for photographic images. It is the most common image format used by digital cameras and other photographic image capturing devices—including mobile phones—and is the most common format for storing and transmitting photographic images on the World Wide Web. It is estimated that over 90% of the world's digital images are stored in the JPEG format.
JPEG typically achieves 10 to 1 compression for photographic images with little perceivable loss in image quality. Other image compression algorithms have since been developed that provide additional compression gains over JPEG. Notable among them is the JPEG 2000 still image compression standard, standardized by the Joint Photographic Experts Group in 2000. However, the world of digital images still revolves around JPEG and has yet to migrate to the new image codecs. Part of the reason for this loyalty to JPEG is the simple, fast, yet efficient algorithm that JPEG provides.
One of the challenges of research in image compression is to come up with simple image codecs that provide fast yet efficient implementations of image compression—providing higher compression gains than JPEG but at the speed and complexity of the simple JPEG algorithm.
Thus, it is desirable to provide a technique that boosts up the compression gains of JPEG without adding much to the cost of complexity of the system and it is to this end that the system and method described below are directed.